In the detergent industries, recently, methods for producing powder detergents having relatively high bulk densities are remarked. Such powdery detergents containing anionic surfactants, such as alkylbenzenesulfonates, are prepared in situ neutralization of an acid precursor of the anionic surfactant with an alkali, such as sodium hydroxide, sodium carbonate, or the like.
For instance, Japanese Patent Laid-Open No. 60-72999 and GB-2,166,452B disclose a process comprising the steps water of blending deterging action components, a sulfonic acid and sodium carbonate, with water with a strong shearing device; cooling the resulting solid substances to 40° C. or lower; finely pulverizing the cooled product; and then forming the fine powders into granules. This method is a typical one of those conventionally proposed methods, in which the neutralization reaction product is a doughy mass, which necessitates a kneading device, such as a kneader, capable of supplying extremely large energy required for the neutralization reaction.
GB-1,369,269 discloses a method for producing an anionic detergent comprising vigorously mixing deterging action components which are a sulfonic acid and sodium carbonate powder by using a mixer equipped with a shearing device, such as Lödige PLOUGH SHARE Mixer. By this method, in order to obtain products of particulate forms, not a doughy mass, it is necessary to blow a gas stream into the two-component mixture mentioned above, to thereby suitably make the reaction substances flowable and blend the reaction mixture. In order to carry out this treatment, the mixer has to be made notably complicated. Also, since water serving to accelerate the neutralization reaction is not added, the progress of this reaction is mild, so that relatively coarse products are formed.
Japanese Patent Laid-Open No. 3-33199 discloses a method of producing a detergent composition comprising the steps of dry-neutralizing components in a high speed mixer/granulator at a temperature of 55° C. or less, and then adding a liquid binder thereto to carry out granulation. Japanese Patent Laid-Open No. 4-363398 discloses a method of producing a detergent composition comprising the steps of dry-neutralizing components in a high speed mixer/granulator at a temperature of 55° C. or more, and then adding a liquid binder thereto to carry out granulation. Japanese Patent Laid-Open No. 3-146599 discloses a method of producing a detergent composition comprising the steps of dry-neutralizing components in a continuous high speed mixer; then increasing to a high bulk density using a moderate speed mixer; and then cooling and/or drying the resulting product to carry out granulation.
The detergent compositions obtainable by the methods described above include granules having small particle sizes. However, for practical purposes, the yield of the detergent composition comprising granules of an even smaller particle size than those desired is yet to be improved.
Also, in the above methods, such factors in operating conditions as the powder temperature, the water content, the powder blending efficiency, and the like, are optimally selected simply for the purpose of preparing detergent compositions comprising granules having smaller particle sizes, never attempting to fundamentally improve the tackiness ascribed to the anionic surfactants, which causes agglomeration of the granules and formation of coarse granules.
Japanese Unexamined Patent Publication No. 7-503750 discloses a method of producing detergent granules comprising neutralizing an anionic surfactant in an acid form with a granular neutralizing agent (sodium carbonate) of which has 50% by volume of particles of less than 5 μm in diameter in a high shearing mixer.
However, in this publication, no disclosures or suggestions concerning the improvements of the yield of the detergent composition comprising granules having a desired particle size are made.
An object of the present invention is to provide detergent granules with suppressed tackiness and small particle size.
Another object of the present invention is to provide a method for producing the above detergent granules.
Still another object of the present invention is to provide a high-bulk density detergent composition comprising the above detergent granules.
These and other objects of the present invention will be apparent from the following description.